Sedimentary breccias along a temporarily emergent Paleocene/Eocene carbonate ramp, Subatlas area of Marrakech, Morocco

Abstract

The Subatlas zone of Marrakech (Morocco) provides a Paleocene-Eocene (P/E) sedimentary record outcropping in a NE-SW direction along the northern edge of the High Atlas. The present study reveals, for the first time, new sedimentological data across the P/E (Thanetian-Ypresian?) boundary. These data have remained unknown despite numerous studies conducted in this area. The P/E interval deposits belong to the Anmiter Formation, represented by bioclastic and fossiliferous limestones intercalated with claystones, silty-sandy marls, and phosphorites. Cherts, siliciclastic limestones, and dolostones occur sporadically. The deposits exhibit numerous sedimentary gaps, mainly corresponding to hardgrounds and subaerial exposure surfaces. The microfauna is scarce, consisting primarily of a few ostracods and benthic foraminifera. The distribution of litho-microfacies reflects deposition in marine environments ranging from proximal to relatively distal settings (inner to outer ramp). The breccias were formed through three main processes: (i) weathering in the vadose zone, (ii) intense erosion on elevated areas, and (iii) dissolution of rocks in an epikarst landscape. Megabreccia blocks and debris were likely emplaced through dissolution processes, exacerbated by significant fracturing resulting from tectonic instability under conditions of relative sea-level fall. These findings highlight the complex interaction of tectonic, climatic, and diagenetic factors during the Thanetian-Ypresian transition and provide new insights into the geological history of the Subatlas area. Further high-resolution studies, incorporating proxies such as stable isotopes and microfossil analyses, are necessary to refine the P/E boundary events in this area.